Harvey: I am sure you are right, that it will turn out to be some very simple mistake or accident, but I am betting that it will also be something very quirky or unlikely. the JMT junction sign was replaced last year, pointing all the arrows in the correct directions, and John has summited six times now over the past 30 years, so a misdirection at that point seems improbable. The Consultation Lake diversion is also possible, but the outlet stream goes right to Outpost Camp and the access trail goes back the the MWMT. I can't think of any other search even over the whole length of the trail that has gone on this long.
Wherever you go, there you are.